# dlacon(3) [centos man page]

```dlacon.f(3)							      LAPACK							       dlacon.f(3)

NAME
dlacon.f -

SYNOPSIS
Functions/Subroutines
subroutine dlacon (N, V, X, ISGN, EST, KASE)
DLACON estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

Function/Subroutine Documentation
subroutine dlacon (integerN, double precision, dimension( * )V, double precision, dimension( * )X, integer, dimension( * )ISGN, double
precisionEST, integerKASE)
DLACON estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

Purpose:

DLACON estimates the 1-norm of a square, real matrix A.
Reverse communication is used for evaluating matrix-vector products.

Parameters:
N

N is INTEGER
The order of the matrix.  N >= 1.

V

V is DOUBLE PRECISION array, dimension (N)
On the final return, V = A*W,  where  EST = norm(V)/norm(W)
(W is not returned).

X

X is DOUBLE PRECISION array, dimension (N)
On an intermediate return, X should be overwritten by
A * X,   if KASE=1,
A**T * X,  if KASE=2,
and DLACON must be re-called with all the other parameters
unchanged.

ISGN

ISGN is INTEGER array, dimension (N)

EST

EST is DOUBLE PRECISION
On entry with KASE = 1 or 2 and JUMP = 3, EST should be
unchanged from the previous call to DLACON.
On exit, EST is an estimate (a lower bound) for norm(A).

KASE

KASE is INTEGER
On the initial call to DLACON, KASE should be 0.
On an intermediate return, KASE will be 1 or 2, indicating
whether X should be overwritten by A * X  or A**T * X.
On the final return from DLACON, KASE will again be 0.

Author:
Univ. of Tennessee

Univ. of California Berkeley

NAG Ltd.

Date:
September 2012

Contributors:
Nick Higham, University of Manchester.
Originally named SONEST, dated March 16, 1988.

References:
N.J. Higham, 'FORTRAN codes for estimating the one-norm of
a real or complex matrix, with applications to condition estimation', ACM Trans. Math. Soft., vol. 14, no. 4, pp. 381-396, December
1988.

Definition at line 116 of file dlacon.f.

Author
Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.2							  Tue Sep 25 2012						       dlacon.f(3)```

## Check Out this Related Man Page

```dlacn2.f(3)							      LAPACK							       dlacn2.f(3)

NAME
dlacn2.f -

SYNOPSIS
Functions/Subroutines
subroutine dlacn2 (N, V, X, ISGN, EST, KASE, ISAVE)
DLACN2

Function/Subroutine Documentation
subroutine dlacn2 (integerN, double precision, dimension( * )V, double precision, dimension( * )X, integer, dimension( * )ISGN, double
precisionEST, integerKASE, integer, dimension( 3 )ISAVE)
DLACN2

Purpose:

DLACN2 estimates the 1-norm of a square, real matrix A.
Reverse communication is used for evaluating matrix-vector products.

Parameters:
N

N is INTEGER
The order of the matrix.  N >= 1.

V

V is DOUBLE PRECISION array, dimension (N)
On the final return, V = A*W,  where  EST = norm(V)/norm(W)
(W is not returned).

X

X is DOUBLE PRECISION array, dimension (N)
On an intermediate return, X should be overwritten by
A * X,   if KASE=1,
A**T * X,  if KASE=2,
and DLACN2 must be re-called with all the other parameters
unchanged.

ISGN

ISGN is INTEGER array, dimension (N)

EST

EST is DOUBLE PRECISION
On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be
unchanged from the previous call to DLACN2.
On exit, EST is an estimate (a lower bound) for norm(A).

KASE

KASE is INTEGER
On the initial call to DLACN2, KASE should be 0.
On an intermediate return, KASE will be 1 or 2, indicating
whether X should be overwritten by A * X  or A**T * X.
On the final return from DLACN2, KASE will again be 0.

ISAVE

ISAVE is INTEGER array, dimension (3)
ISAVE is used to save variables between calls to DLACN2

Author:
Univ. of Tennessee

Univ. of California Berkeley

NAG Ltd.

Date:
November 2011

Further Details:

Originally named SONEST, dated March 16, 1988.

This is a thread safe version of DLACON, which uses the array ISAVE
in place of a SAVE statement, as follows:

DLACON	   DLACN2
JUMP	  ISAVE(1)
J	  ISAVE(2)
ITER	  ISAVE(3)

Contributors:
Nick Higham, University of Manchester

References:
N.J. Higham, 'FORTRAN codes for estimating the one-norm of
a real or complex matrix, with applications to condition estimation', ACM Trans. Math. Soft., vol. 14, no. 4, pp. 381-396, December
1988.

Definition at line 137 of file dlacn2.f.

Author
Generated automatically by Doxygen for LAPACK from the source code.

Version 3.4.1							  Sun May 26 2013						       dlacn2.f(3)```
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